Abstract

The cochlear microphonic was recorded in response to a 733 Hz tone embedded in noise that was high-pass filtered at 25 different frequencies. The amplitude of the cochlear microphonic increased as the high-pass cutoff frequency of the noise increased. The amplitude growth for a 60 dB SPL tone was steeper and saturated sooner than that of an 80 dB SPL tone. The growth for both signal levels, however, was not entirely cumulative with plateaus occurring at about 4 and 7 mm from the apex. A phenomenological model of the electrical potential in the cochlea that included a hair cell probability function and spiral geometry of the cochlea could account for both the slope of the growth functions and the plateau regions. This suggests that with high-pass-filtered noise, the cochlear microphonic recorded at the round window comes from the electric field generated at the source directed towards the electrode and not down the longitudinal axis of the cochlea.

Received 20 June 2012Revised 19 September 2012Accepted 24 September 2012Published online 08 November 2012

Acknowledgments:

The authors wish to thank Megan Ash, Will Chertoff, and Dianne Durham for developing the anatomical approach to image the cochlea. Also we thank Christopher Neal for his effort to translate the cochlear equations into the three-dimensional structure using autocad. This study was supported by the National Institutes of Health Grant No. R21DC011096 and the Kansas Intellectual and Developmental Disabilities Research Center Grant No. HD002528.